Efficient Visible-Light Photocatalytic Cycloaddition of CO₂and Propylene Oxide Using Reduced Graphene Oxide Supported BiNbO₄

In this study, a series of novel BiNbO4 and BiNbO4/reduced graphene oxide (BiNbO4/r-GO) visible-light photocatalysts were prepared. Pure BiNbO4 was prepared by simple co-precipitation; on the other hand, BiNbO4/r-GO composites were prepared by simple mechanical mixing, followed by hydrothermal treatment. The effect of r-GO on the structural, surface morphological, and optical properties of the prepared photocatalysts was investigated using ultraviolet-visible (UV-vis) diffuse reflectance spectroscopy (UV-vis DRS), powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET) for the determination of the specific surface area and porosity and energy-dispersive X-ray spectroscopy (EDX) for determining the elemental composition. A red shift in optical band gap measurements was observed with the increasing r-GO mass percentage in the prepared BiNbO4/r-GO composites. Photocatalytic activities of pure BiNbO4 and the composites were evaluated using the photocatalytic cycloaddition of carbon dioxide to propylene oxide as a model reaction. All the prepared photocatalysts produced cyclic propylene carbonate selectively with no polymeric material observed. The highest photocatalytic efficiency was achieved using BiNbO4/5% r-GO composite photocatalyst, where the mass percentage of r-GO was 5%.